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Merge pull request #14826 from fungiboletus/patch-2 

tsdb documentation: More details about Chunks
pull/15246/merge
Bryan Boreham 2024-12-04 13:20:57 +00:00 committed by GitHub
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tsdb/docs/format/chunks.md
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@ -25,20 +25,20 @@ in-file offset (lower 4 bytes) and segment sequence number (upper 4 bytes).
└──────────────────────────────┘
```
# Chunk
```
┌───────────────┬───────────────────┬─────────────┬────────────────┐
│ len <uvarint> │ encoding <1 byte> │ data <data> │ CRC32 <4 byte> │
└───────────────┴───────────────────┴─────────────┴────────────────┘
┌───────────────┬───────────────────┬─────────────┬───────────────────┐
│ len <uvarint> │ encoding <1 byte> │ data <data> │ checksum <4 byte> │
└───────────────┴───────────────────┴─────────────┴───────────────────┘
```
Notes:
* `<uvarint>` has 1 to 10 bytes.
* `encoding`: Currently either `XOR`, `histogram`, or `floathistogram`, see
[code for numerical values](https://github.com/prometheus/prometheus/blob/02d0de9987ad99dee5de21853715954fadb3239f/tsdb/chunkenc/chunk.go#L28-L47).
* `len`: Chunk size in bytes. 1 to 10 bytes long using the [`<uvarint>` encoding](https://go.dev/src/encoding/binary/varint.go).
* `encoding`: Currently either `XOR`, `histogram`, or `floathistogram`, see [code for numerical values](https://github.com/prometheus/prometheus/blob/02d0de9987ad99dee5de21853715954fadb3239f/tsdb/chunkenc/chunk.go#L28-L47).
* `data`: See below for each encoding.
* `checksum`: Checksum of `encoding` and `data`. It's a [cyclic redudancy check](https://en.wikipedia.org/wiki/Cyclic_redundancy_check) with the Castagnoli polynomial, serialised as an unsigned 32 bits big endian number. Can be refered as a `CRC-32C`.
## XOR chunk data
@ -177,7 +177,6 @@ the encoding will therefore result in a short varbit representation. The upper
bound of 33554430 is picked so that the varbit encoded value will take at most
4 bytes.
## Float histogram chunk data
Float histograms have the same layout as histograms apart from the encoding of samples.